Goniometric sensor

ABSTRACT

A goniometric sensor ( 1 ) for measuring the relative rotation of two objects ( 20, 25 ) includes a flexible elongated element ( 2 ) whose respective ends are connected to the two objects ( 20, 25 ) and during whose bending the length variation ΔL is determined of one of the fibers ( 15 ) not located at the neutral axis (10). This length variation ΔL is directly proportional to the relative rotation (α) between the two bodies ( 20, 25 ) multiplied for the eccentricity (e) of the fiber ( 15 ) with respect to the neutral axis ( 10 ). Therefore, it is possible to determine easily the relative rotation (α) by knowing the length of rest L and the eccentricity (e) with respect to the neutral axis ( 10 ) and to measure the length variation ΔL of fiber ( 15 ), for example measuring the movement of an end of a cable located in a hole that contains fiber ( 15 ).

FIELD OF THE INVENTION

The present invention generally relates to a device for determining the angle of rotation of an object moving in space with respect to a reference object.

In particular, the invention relates to a device for determining the relative angular position of two bodies moving in space with respect to each other.

BACKGROUND OF THE INVENTION

Various electromechanical sensors exist used for measuring angular position between two bodies rotating with respect to each other. However, such sensors usually measure the relative angular position of bodies mechanically connected by rigid joints, for example the steering wheel and the transmission shaft of a car.

The nature of the sensors mentioned above remarkably limits the applicability in special fields such as, for example, virtual reality or the design of artificial prosthesis in medicine.

In particular, such sensors are not suitable in fields that, owing to technological progress, have recently captured the attention of many researchers, i.e. acquisition and analysis of movement of human body parts. By using absolute position data of single points of the human body or angular relative positions between two adjacent limbs, a digital model of the human body can be created.

The known sensors suitable for this particular fields depend on the type of application and on the limbs that have to be monitored.

In particular, the limbs with greater volume, such as arms and legs of a human, have few degrees of freedom and the devices used for detecting their motion usually have higher weight and encumbrance and require a higher rate of precision. The limbs with smaller volume, instead, such as the fingers of the hand that have a higher number of degrees of freedom, cannot be monitored with heavy and bulky devices and require less precision.

The known sensors used for tracking the motion of the limbs of the human body are usually of magnetic, optical, ultrasonic or mechanical nature.

Among them, two main categories of sensors exist:

-   -   1) sensors that do not require a mechanical connection between         the reference object and the object to be monitored.     -   2) sensors that require a mechanical connection between the         reference object and the object to be monitored.

To the first category the following belong:

Magnetic sensors, which require one or more transmitters for creating a magnetic field in a determined workspace. In particular, they have high costs and have the further drawback of being particularly sensitive to the presence of metal that can distort the magnetic field.

Optical sensors, which require optical markers, either active or reflective, whose light is captured allowing a computer to calculate its position. Usually, the optical devices are less bulky than the magnetic, but their functionality can be affected by parts of the body that cross accidentally the path of the light. Another drawback of the optical devices are high costs and the need for a post-processing of the measured data, as well as the long set up time for calibrating the measuring equipment.

To the second category the following belong:

Sensors of mechanical type, based on strain gauges embedded in a flexible support structure, providing the angle of rotation of the sensor-support assembly. Their performances are high but they have reliability problems and a high cost;

Sensors based on optical fibres, which measure the variation of intensity of a light beam projected in an optical fibre. This measure reveals the angle of rotation of the sensor support. Such sensors have a relatively low cost but have reliability problems and low measuring precision.

SUMMARY OF THE INVENTION

It is therefore object of the present invention to provide a goniometric sensor for determining the relative angular position of two objects.

It is another object of the present invention to provide a goniometric sensor that is structurally simple and cost effective.

It is a further objective of the present invention to provide a goniometric sensor capable of overcoming the drawbacks of the devices of prior art.

These and other objectives are accomplished by the goniometric sensor, according to the present invention, for measuring the relative rotation of a first object and a second object whose characteristic is that it comprises:

-   -   a flexible elongated element that extends between said first and         said second object, said element having a neutral axis, which         does not change its own length when bending, and at least one         fibre located apart from said neutral axis and that extends from         said first to said second object;     -   means for measuring the length variation of said fibre as the         relative rotation varies between said first and said second         object, said relative rotation being proportional to said length         variation.

Preferably, the bending of said flexible elongated element is carried out in a predetermined plane.

Advantageously, said or each fibre is associated to a channel that runs the flexible elongated element along said fibre, in said channel a medium being present suitable for transmitting a signal to said means for measuring said length variation.

In particular, the medium suitable for transmitting said signal is a cable connected to a first point of the channel and wherein said means for measuring record the movement of the cable at a second point of the channel.

Advantageously, said cable has one end connected to an end of the channel and has the other end freely moving, whereby the sensing device measures the movement of the free moving end with respect to the channel.

Advantageously, said means for measuring the length variation of the fibre are chosen among: Hall effect sensors, optical sensors, magnetic induction sensors, piezoelectric sensors, etc.

According to a possible alternative embodiment, the flexible elongated element has at least one channel closed at the ends that is eccentric with respect to the neutral axis and in which a certain amount of a compressible fluid is contained, for example air, at a measured pressure. A bending action of the flexible elongated element causes a pressure variation of the fluid in thechannel, detected by means for measuring the pressure variation and converted into a measure of the length variation proportional to the detected pressure variation.

In a further embodiment, the eccentric tubular channel is closed at one end and is filled with an amount of incompressible fluid, a position reference element being slidingly arranged at the other end. In this case, the bending of the flexible elongated element causes a variation of the distribution of the incompressible fluid in the tubular channel and then a movement of the reference element, which is detected by said means for measuring the variation of the length.

According to a particular aspect of the invention, the goniometric sensor as above described can be advantageously mounted on a data glove. In particular, at each finger of the glove at least one goniometric sensor is arranged according to the invention, having an end constrained to the back of the hand in order to extend for at least one portion of the finger same. In this way, it is possible to measure relative angular movements of the different fingers of the glove. The goniometric data glove thus obtained can have applications, for example, in the field of virtual reality, in the medical field, etc. For example, two or three goniometric sensors can be used for each finger of the hand for measuring the flexo-extension of each phalanx, and a goniometric sensor rotated of 90° about its own axis can be used for measuring the ab-adduction of the fingers with respect to the hand.

Another particular aspect of the invention relates to a device for measuring the rotation of the wrist of an arm comprising at least one goniometric sensor as above described. In particular, said or each goniometric sensor is arranged with an end integral to the wrist and with the other end constrained to a second point of the arm that during the rotation of the wrist remains substantially fixed, for example the elbow. Therefore, the goniometric sensor measures the rotation of the wrist with respect to the second point of the arm. Furthermore, two sensors can be used at the wrist, which operate in two planes orthogonal to each other and that contain the axis of the forearm. This solution is suitable for the acquisition of the data relating respectively to the flexo-extension and the ab/adduction of the hand with respect to the forearm.

A further particular aspect of the invention provides a plurality of goniometric sensors as above described arranged in series along a rope that connects an object in movement to a reference point. This way, a device is obtained for fully localizing and monitoring the object position, by integrating the results of each single goniometric sensor using a computing unit, assuming a constant curvature of the rope in each portion including a single sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and the advantages. of the goniometric sensor according to the present invention will be made clearer with the following description of an embodiment thereof, exemplifying but not limitative, with reference to the attached drawings, wherein:

FIG. 1 shows a top plan view of a goniometric sensor according to the invention;

FIG. 2 shows a longitudinal sectional view according to arrows II-II of the goniometric sensor of FIG. 1;

FIG. 3 shows a side view of the goniometric sensor of FIG. 1;

FIGS. 4 and 5 show a cross sectional view of the goniometric sensor of FIG. 1 respectively according to arrows IV-IV and V-V;

FIGS. 6 and 7 show the goniometric sensor of FIG. 1 in a perspective view respectively exploded and assembled;

FIG. 8 shows a top plan view of an alternative embodiment of the sensor of FIG. 1;

FIG. 9 shows a longitudinal sectional view according to arrows IX-IX of the goniometric sensor of FIG. 8;

FIG. 10 shows diagrammatically the working principle of the goniometric sensor of FIG. 1;

FIGS. 11 and 12 show diagrammatically a further alternative embodiment of the goniometric sensor of FIG. 1;

FIG. 13 shows a first possible application of the goniometric sensor of FIG. 1, in particular, a glove for goniometric measures or data glove;

FIGS. 14 to 16 show a second possible application of the goniometric sensor of FIG. 1, in particular a device for measuring angular movements of a wrist;

FIG. 17 shows a third possible application of the goniometric sensor of FIG. 1, in particular, an apparatus for tracking movements and localizing an object in movement.

DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to FIGS. 1 and 2, a sensor for goniometric measures 1, according to the present invention, measures the relative rotation of two bodies 20 and 25, symbolically indicated with circles in FIG. 1.

In particular, sensor 1 comprises a flexible elongated element 2 whose respective ends are connected to bodies 20 and 25. Goniometric sensor 1 has an axis of symmetry 10 that is the same of element 2. At the bending of element 2, the axis 10 becomes also neutral axis, i.e. it has fibres that do not lengthen or shorten when bending. Furthermore, numeral 15 indicates a generic line that is eccentric with respect to the neutral axis.

When bodies 20 and 25 rotate with respect to each other, flexible elongated element 2 is subject to a bending that produces a length variation of the fibres different from the neutral axis 10. In particular, a fibre coincident to eccentric line 15 is subject to a length variation ΔL (FIG. 10). It must be noted that the neutral axis changes according to the beam geometry, and then it does not always coincide with the axis of symmetry.

Such length variation ΔL is directly proportional to the relative rotation between the two bodies 20 and 25, and in particular it is proportional to the product of the angle to measure (α) and of the eccentricity (e) with respect to the neutral axis. Therefore, it is possible to determine easily the relative rotation α by knowing the eccentricity of the cable with respect to the neutral axis 10 and measuring the length variation ΔL.

It must be noted that if a rotation according to an angle α of the flexible elongated element 2 causes a lengthening ΔL of fibre 15, an opposite rotation equal to −α of the flexible elongated element 2 causes a shortening −ΔL of the same fibre 15. This is very advantageous in order to double the range of measurable angles.

In a first embodiment of the invention (FIG. 2-7) the length variation of fibre 15 is determined by a sensor 7, for example a Hall effect sensor, which detects the movement of the end of a cable 5 located in a channel 4 made at the end of element 2.

In the case shown in the figures, cable 5 has an end 5 a connected to an end of elongated element 2 and the other end 5 b connected to a magnet 6 sliding in an enlarged portion 4 a of channel 4. Therefore, a relative angular movement of the two bodies 20 and 25 causes the above described variation ΔL of the length of fibre 15 that forces the cable 5 to slide in channel 4 and then causes magnet 6 to slide in the enlarged portion 4 a of a corresponding portion. The movement of magnet 6, and then the variation ΔL of the length of fibre 15 is detected by sensor 7 located near magnet 6 same and then encoded into a measure of the relative rotation α, exploiting the above cited equation between eccentricity, angle and lengthening.

As shown in FIG. 6 in an exploded view, at the neutral axis 10 of goniometric sensor 1 a stiffening element 30 can be located, in particular if the elongated element should have a high axial stiffness.

In FIGS. 7 to 9 an alternative embodiment is shown of goniometric sensor 1, wherein in the enlarged portion 4 a of channel 4 in addition to magnet 6 a second magnet 6′ is arranged having mainly the function of keeping stretched cable 5 attracting magnet 6 when detecting the variation of its length by sensor 7.

Alternatively to FIGS. 1 to 9 above described, in which sensor of presence 7 is shown arranged in a plane parallel to channel 4, the sensor of presence can be arranged, according to an embodiment not shown, in a plane orthogonal to the axis of channel 4 same.

Elongated element 2 shown in FIGS. 1-9 can be made, advantageously, in two different parts: a first elongated portion 2 and a head 3 to it releasably engageable. On releasable head 3 sensor 7 is mounted and a channel is made, co-axial to channel 4 of elongated element 2, in which sliding magnet 6 is arranged.

The alternative embodiment of the goniometric sensor 1 shown in FIGS. 11 and 12 comprises, instead, a channel 4 b closed at the ends where a measured amount of an incompressible fluid is present, for example water, contacting a reference element 11. In this case, the bending of elongated element 2 causes the lengthening or shortening of the channel at line 15 and, therefore, a variation of the inner volume of channel 4 b. This causes a variation of the distribution of the incompressible fluid in channel 4 b and then a movement of reference element 11 of a, entity ΔL measurable with mechanical, optical, magnetic means or of other kind.

Alternatively, in channel 4 b a compressible fluid can be inserted at a certain starting pressure Po. In this case the variation of the length of fibre 15, i.e. the variation then of the volume of channel 4 b, causes a pressure variation ΔP that is detected and converted into a measure of the relative rotation of the two bodies 20 and 25.

In FIGS. 13 to 17 some possible applications are shown of goniometric sensor 1, as above described.

In particular, in FIG. 13 a glove 50 is shown arranged with a plurality of goniometric sensors on each finger 51. This way, goniometric measures can be easily made necessary for different applications for example, in the field of virtual reality, or in the medical field for prosthesis designing or for making easier the rehabilitation of a limb subject to surgery causing the hand to follow predetermined movements. In the example, two goniometric sensors 1 are used for each finger 51 of the hand for measuring the flexo-extension of the phalanxs, and a goniometric sensor 1′ is also used rotated of 90° about its own axis for measuring the ab/adduction of the fingers 51 with respect to the hand. Each sensor has then an end constrained to the back of the hand in 52 and extends for at least one portion of the finger 51 same.

In FIGS. 14 to 16 a goniometric sensor 1 is shown used for measuring the rotation of a wrist 65 of a hand. In particular, the goniometric sensor 1 is arranged with an end 1 a integral to the wrist 65 and with the other end 1 b connected to a rod 60 constrained at the elbow and then the rotation is determined of the wrist 65 with respect to the elbow. Furthermore, two further sensors 1 are used at the wrist along two different directions 66 and 67 belonging to two planes orthogonal to each other that contain the axis of the forearm 69. The sensor arranged in direction 66, in particular, detects the flexo-extension of the hand 68 with respect to forearm, whereas the sensor in the direction 67 detects the ab/adduction of the hand 68 always with respect to forearm 69.

Another particular application of the invention is shown in FIG. 17 and-provides the use of a plurality of goniometric sensors S₁ . . . S_(n) arranged along a connecting cable 75 for monitoring movements and then localizing instantly “a tunnelling machine” 70 for explorations of the underground. In this case, the exact localisation of the object 70 is determined by integrating the measured data of the single goniometric sensors S₁ . . . S_(n). In particular, each goniometric sensor provides for each portion a couple of data of position, for example Δx_(i), Δy_(i), relative to the movement in that portion therefore, adding the data relative to the single portions and knowing instantly the length of the cable 75 unwound allows to determine the spatial coordinates (x, y, z) of the object 70 monitored: $x = {\sum\limits_{i = n}^{i = 0}{\Delta\quad x_{i}}}$ $y = {\sum\limits_{i = n}^{i = 0}{\Delta\quad y_{i}}}$ considering the single reference system rotated.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. 

1. Goniometric sensor for measuring the relative rotation of a first object with respect to a second object characterised in that it comprises: a flexible elongated element that extends between said first and said second object, said element having a neutral axis, which does not change its own length when bending, and at least one fibre spaced apart from said neutral axis that extends from said first to said second object; means for measuring the length variation of said fibre as the relative rotation varies between said first and said second object, said relative rotation being proportional to said length variation.
 2. Goniometric sensor, according to claim 1, wherein said or each fibre is associated to a channel that runs along said fibre of said elongated flexible element, in said channel a medium being present suitable for transmitting a signal to said means for measuring said length variation.
 3. Goniometric sensor, according to claim 1, wherein said medium suitable for transmitting is a cable connected to a first point of the channel, and wherein said means for measuring records the movement of said cable at a second point of said channel.
 4. Goniometric sensor, according to claim 3, wherein said cable has an end connected to an end of said channel and the other end freely moving, said means for measuring recording the movement of the other end of the cable with respect to the other end of the channel.
 5. Goniometric sensor, according to claim 1, wherein said means for measuring are chosen among Hall effect sensors, optical sensors, magnetic induction sensors, piezoelectric sensors, etc.
 6. Goniometric sensor, according to claim 1, wherein said bending of said flexible elongated element is carried out in a predetermined plane.
 7. Goniometric sensor, according to claim 1, wherein said flexible elongated element has at least one eccentric tubular channel shifted from said neutral axis and closed at the ends, said tubular channel containing a certain amount of a compressible fluid at a measured starting pressure whereby said bending of the flexible elongated element causes a pressure variation of said fluid detected by said means for measuring.
 8. Goniometric sensor, according to claim 1, wherein said flexible elongated element has at least one eccentric tubular channel with an amount of incompressible fluid, a position reference element being arranged at the other end, said bending of said flexible elongated element causing a variation of the distribution of the incompressible fluid in the tubular channel and then a movement of the reference element that is detected by said means for measuring.
 9. Glove for goniometric measures characterised in that it comprises at least a goniometric sensor according claim 1, said goniometric sensor being arranged with an end constrained to the back of the glove and extending for at least one portion of said finger or located completely on the finger.
 10. Glove according to claim 9, wherein at least two goniometric sensors are used for each finger of the hand for measuring the flexo-extension of the phalanxs, and a goniometric sensor rotated of 90° about its own axis for measuring the ab/adduction of the fingers with respect to the hand.
 11. Device for measuring the rotation of a wrist characterised in that it comprises at least one goniometric sensor, according to claim 1, arranged with an end integral to said wrist and with the other end constrained to a point of the arm that during said rotation of said wrist remains substantially fixed, said device detecting the relative rotation of said wrist with respect to said second point.
 12. Device for measuring the rotation of a wrist according to claim 11, comprising furthermore two sensors at the wrist, which operate in two planes orthogonal to each other and that contain the axis of the forearm, for detecting respectively the flexo-extension and the ab/adduction of the hand with respect to forearm.
 13. Device for localizing an object in the space by means of goniometric measures characterised in that it comprises a plurality of goniometric sensors, according to claim 1, arranged in series, said localisation being executed integrating the data obtained by the single goniometric sensors by means of a computing unit. 